Is it time to replace my slow IMac?

If you need a reliable computer for a new business then this is a great time to get a new computer. I would suggest either a Macbook or a Mac Mini. (The iMac line has not been updated since April 2021). If necessary you could use external storage to keep the photos.

If you wish to keep your old 2013 as a secondary computer for personal use you can fix most of the performance issues by purchasing an external USB 3.0 SSD and reinstalling MacOS onto that.

Your hard drive is failing. Though it would be possible to replace it or go to an external SSD instead, I'm not sure I'd invest the money in that.

If money is tight, then I'd go the external SSD route. At least it would be usable when you do get around to replacing your Mac.

Otherwise, bake sure you have good backups! Your hard drive could fail completely at any moment.

I agree with the others that it might be time to seriously consider a new Mac. If budget is a concern look at Apple's refurbished Macs. Since the new iMacs and Minis can have RAM upgraded after purchase be sure to get at least a minimum of 15 GB of RAM and a 1 TB boot drive. You'll have to look carefully to find one with those specs.

Since you're running Catalina you don't have to worry about 32 bit apps not working. That was addressed when you went to Catalina.

If you go with a new Mac Mini look for a 3rd party monitor that is 4K and has built in speakers. LG has some pretty good 27 and 32 inch models.

Good luck.

Yes, however, it’s best that you research your new Mac at the Apple Store both online & in-store and come back with specific questions on whichever model you’re interested in.